In recent years, the interest in electronic transactions has increased significantly, especially concurrently with the impact of the Internet. Security matters have been focused, and different systems and standards have been suggested to guarantee the security in connection with electronic transmission of transaction messages. A matter that has attracted a lot of interest is how to protect, for instance, credit card numbers transmitted via the Internet in connection with Internet shopping. What the systems and standards proposed have in common is that they are based either on the condition that sensitive information that may be misused, for instance a credit card number, is not to be transmitted via the communications network, or on the condition that such sensitive information is to be transmitted in encrypted form. In both alternatives, the relatively complicated administrative routines and system configurations etc. are focused, which, as will be appreciated, results in restrictions and obstacles to a more general use.